In order that the welding is of good quality, that is to say in order that one obtains a joint which is tight with respect to gaseous fluids and which has satisfactory mechanical strength, the electrical power and the heating time must be wisely chosen. In addition, the outer wall of the tubes to be welded must be previously cleaned: it is necessary to scrape the surface in order to remove the superficial layer of oxidized material which has been changed by aging. In fact, the storage of the tubes is sometimes long, which exposes the outer wall of the tubes to all types of attack.
If this cleaning operation, in fact scraping, is not carried out carefully, the connection of the two tubes has every chance of proving unsuitable, i.e., having an appreciable danger of leakage in the long term and/or poor mechanical behavior. Drawbacks of this type, even to the point of risk, are not acceptable and may be the cause of catastrophes.
It should be noted that the scraping operation is hard and not without risks for the worker responsible for carrying it out.